1. Field of the Invention
The invention relates to a method for measuring the output current of a clocked half-bridge circuit in which semiconductor switches located in half-bridge sections are alternately opened or closed in push-pull operation thereby causing a controllable current flow to occur in output current circuit, whereby the amperage of the current flowing through a first semiconductor switch is measured. The invention also relates to a measuring device to measure the output current of a clocked half-bridge circuit that has at least one half-bridge having two half-bridge sections connected in series, whose connection node is connected to an output connection; and a first semiconductor switch is disposed in a first half-bridge section, and a second semiconductor switch is disposed in a second half-bridge section, and said semiconductor switches can be controlled in push-pull operation by means of a control device, and with an alternating-current controller whose output is connected to a measured-signal input of the measured-value signal conditioning device, which has a measurement output for an output current measurement signal.
2. Description of Related Art
A method of this type and a measuring device of this type are disclosed in DE 41 17 505 C2. To control the winding of an electric motor, the measuring device has a half-bridge circuit having two half-bridge sections connected in series that are connected to a connection node on an output circuit that contains the motor winding. A series circuit comprising a first semiconductor switch and a shunt is located in a first half-bridge section, and a second semiconductor switch is located in a second half-bridge section. The semiconductor switches are controlled in alternation in a push-pull configuration by means of a control device. Each time during a first operating state the first semiconductor switch is closed, and the second semiconductor switch is closed during a second operating state. In each of the first operating states, one measured value for the current flowing through the first semiconductor switch is acquired with the aid of the shunt. This measured value provides the measurement result for the output current. In the first operating states, a second measured value is also acquired for the alternating current in the output circuit by means of an alternating-current converter.
This measured value is added to the first measured value. Then the result of this addition is inverted and saved. In the second operating state a measured value for the alternating current flowing in the output circuit is acquired and added to the saved value. The resulting total forms the measurement result in the second operating state.
The measuring device has proven to be effective in actual practice, mainly because it makes it possible to measure current in an output circuit that has a high electrical potential compared with the measurement circuit. However, a disadvantage of the measuring device is that the use of the shunt means that there is no electrical isolation between the power circuit and the measurement circuit. Moreover, the power loss in the shunt is undesirable.
Thus, the object of the invention is to create a method of the type referred to above that permits the output current to be measured in a simple, economical manner with low losses and, if possible, with electrical isolation. The object is also to disclose a measuring device of the type referred to above to perform the method.